How much should a person drink in 24 hours?

November 18, 2025 •

3 min read

According to the U.S. National Academies of Sciences, Engineering, and Medicine, the average adequate daily fluid intake is about 15.5 cups (3.7 liters) for men and 11.5 cups (2.7 liters) for women, but how much should a person drink in 24 hours depends on many factors. This amount can vary significantly based on individual needs.

Quick Summary

This guide outlines the factors influencing daily fluid intake, recommended quantities for different demographics, the symptoms and dangers of dehydration and overhydration, and practical tips for staying hydrated.

Key Points

Fluid intake varies by person: General guidelines exist, but individual needs depend on factors like activity level, climate, and health.
Listen to your body: Drink when you feel thirsty, but also be aware that this can be a late signal, especially in older adults.
Monitor urine color: Pale yellow urine indicates good hydration; clear suggests potential overhydration, while dark yellow points to dehydration.
Stay aware of overhydration risks: Although rare, drinking excessive amounts of water can dilute sodium levels in the blood, leading to hyponatremia.
Consider food sources: About 20% of your daily fluid intake comes from foods, particularly fruits and vegetables with high water content.
Be proactive: For optimal hydration, drink fluids consistently throughout the day rather than consuming large quantities at once.

Water is a vital nutrient, essential for almost every bodily function, from carrying nutrients and flushing waste to regulating body temperature. While the often-quoted 'eight glasses a day' rule is a simple guideline, a person's fluid requirements are highly individual. The total amount of water consumed in a 24-hour period comes from plain water, other beverages, and water-rich foods.

The Average Daily Fluid Intake

For a healthy adult living in a temperate climate, the U.S. National Academies of Sciences, Engineering, and Medicine provides general Adequate Intake (AI) guidelines for total fluid from all sources:

For men: Approximately 15.5 cups (3.7 liters) of total fluids daily.
For women: Approximately 11.5 cups (2.7 liters) of total fluids daily. These figures include fluids from all beverages and foods. For example, many fruits and vegetables contain a high percentage of water and contribute significantly to overall hydration.

How to Customize Your Fluid Needs

Several factors can increase or decrease your body's fluid needs. It's crucial to adjust your intake based on your unique circumstances.

Exercise: Any activity that causes you to sweat requires extra water to cover fluid loss. Athletes engaged in high-intensity exercise may need to replace electrolytes as well as water.
Environment: Hot, humid, or high-altitude environments can increase sweating and lead to higher fluid needs.
Overall Health: Illnesses involving fever, vomiting, or diarrhea cause fluid loss and necessitate higher intake. Conditions like kidney or heart problems may require a doctor's guidance on fluid intake.
Pregnancy and Breastfeeding: Pregnant or breastfeeding individuals need additional fluids to stay hydrated.
Age: The body's fluid reserve becomes smaller with age, and the thirst sense can diminish, putting older adults at higher risk of dehydration. Infants and young children also require specific fluid intake levels based on their age and body weight.
Diet: A diet high in fiber requires more water to prevent constipation. Similarly, consuming high-sodium foods increases the body's fluid needs.

The Dangers of Dehydration and Overhydration

Maintaining a healthy fluid balance is key. Both dehydration and overhydration can cause significant health problems.

Comparison of Dehydration vs. Overhydration


Feature	Dehydration (Too Little Water)	Overhydration (Too Much Water)
Cause	Not enough fluid intake, excessive sweating, vomiting, diarrhea.	Drinking excessive amounts of fluid in a short period, sometimes during endurance exercise.
Key Symptom	Thirst, dark yellow urine, infrequent urination.	Headache, nausea, feeling confused or disoriented.
Urine Color	Dark yellow or amber.	Clear or colorless.
Other Signs	Dry mouth, lips, and tongue; fatigue; dizziness; sunken eyes.	Swelling in feet, hands, or lips; muscle cramps or weakness.
Severe Consequences	Kidney stones, kidney failure, heatstroke.	Hyponatremia (low sodium levels), seizures, coma.
At-Risk Individuals	Infants, older adults, athletes, and the sick.	Endurance athletes, those with certain health conditions.

Practical Tips for Staying Properly Hydrated

Consistent, moderate fluid intake throughout the day is the best approach to hydration. Here are some strategies to help you stay on track:

Listen to your body: While thirst is a late sign of dehydration, it is still the body's natural cue to drink.
Monitor your urine color: Your urine should be pale yellow. Clear urine may indicate overhydration, while dark yellow urine is a sign of dehydration.
Carry a water bottle: Keeping a reusable bottle with you makes it easier to track and increase your fluid intake throughout the day.
Drink with meals: Habitually drinking a glass of water with each meal and snack can help boost your total intake.
Infuse your water: Add flavor with fresh fruit slices, cucumber, or herbs to make water more appealing.
Eat water-rich foods: Fruits and vegetables like watermelon, strawberries, and spinach contribute significantly to your fluid intake.

Conclusion

While a general recommendation can offer a starting point, understanding your personal fluid needs is the most effective way to stay hydrated and healthy. Pay attention to your body's signals, the color of your urine, and environmental factors. By drinking consistently throughout the day and listening to your body, you can maintain optimal hydration, supporting all of your body's essential functions for overall wellness. For more on the benefits of healthy hydration, see the American Heart Association's resource on the topic.

Frequently Asked Questions

For an average, healthy adult in a temperate climate, general guidelines suggest a total daily fluid intake of about 15.5 cups (3.7 liters) for men and 11.5 cups (2.7 liters) for women, sourced from beverages and food.

Yes, caffeinated drinks contribute to your daily fluid intake. While caffeine is a diuretic, studies show that moderate consumption does not negatively impact overall hydration.

Signs of dehydration include extreme thirst, dark yellow or strong-smelling urine, infrequent urination, fatigue, dizziness, and a dry mouth.

Yes, although it's rare, drinking too much water in a short time can cause overhydration and hyponatremia (low blood sodium). It is most commonly a risk for endurance athletes or individuals with certain medical conditions.

You can add flavor to water with fruit, cucumber, or herbs. Other hydrating options include low-sugar fruit juice, milk, herbal tea, and water-rich foods like fruits and soups.

Early symptoms of overhydration can include headaches, nausea, muscle cramps, and persistent urination, especially at night. A clear or colorless urine can also be an indicator.

The amount depends on exercise intensity, duration, and climate. Weighing yourself before and after a workout can help determine fluid loss. A common guideline is to drink 16 to 24 ounces of water for every pound lost during exercise.